The invention herein relates to thermal insulation. More particularly it relates to the thermal insulation useful for the insulation of pipe flanges and fittings.
In any oil refinery, chemical plant, power plant, or similar facility there are dozens or hundreds of pipe lines carrying high temperature fluids such as crude oil and petroleum products, water, steam and the like. Such lines normally have flanges or fittings every few feet of pipe run length. In the past it has been common to insulate the runs of straight or curved pipe with conventional solid or fibrous thermal insulation units.
Insulation of flanges and fittings has posed severe problems, however. In the first place, flanges and fittings present irregular shapes to which conventional semi-cylindrical or flat block pipe insulations do not conform. Thus resort has been had to specially molded insulations which are preformed to the irregular configuration of the specific fitting to be insulated; typical of such molded insulations is that shown in U.S. Pat. No. 3,367,358. Another alternative method of insulating flanges or fittings has been by using troweled or sprayed cements. While this avoids the problem of having to make individual molded insulations for each separate fitting, it has the disadvantages that the cemented insulations cannot be readily removed from the flange or fitting. The cement also tends to foul moving parts of fittings and bolted connections of flanges. Further, it is difficult to get relative uniformity of thickness of the cemented insulations and insulating effect is therefore variable.
An overriding consideration with both flanges and fittings has been that they frequently leak, particularly when the fluid inside the pipe is at a high pressure. With both molded insulations and cemented insulations such fluid leakage is trapped within the insulation where it can corrode or otherwise deteriorate both the pipe and the insulation. Where high pressure pipes are concerned, such internal corrosion is extremely hazardous, for it can substantially weaken a pipe and make it prone to explosion under pressure before any observer would become aware that leakage was occurring.
In view of the difficulty of insulating flanges and fittings, and more importantly because of the danger of internal leakage and corrosion around such flanges and fittings, most oil refiners, chemical plant operators, power plant operators and other users of such piping have elected to leave flanges and fittings uninsulated. This facilitates early leak detection and simplifies repair or replacement of leaking flanges or fittings. The economic and thermal cost of leaving the flanges or fittings uninsulated is extremely high, however. For instance it can be calculated from a recent article by Cordero, "The Cost of Missing Pipe Insulation," Chemical Engineering, 77-78 (Feb. 11, 1977) that the annual heat loss from a single uninsulated flanged coupling joining two 6" 400 psi steel pipes with a pipe surface temperature 400.degree. F. above ambient is on the order of 90 million BTU's. When it is realized that a single typical oil refinery will have hundreds or thousands of such flanges and that fuel costs can be one dollar or more per million BTU's, the obvious cost in thermal energy wastage and dollar value throughout the United States and the world becomes staggering. Consequently, it is of the utmost importance to develop an efficient flange and fitting insulation which can be readily and easily installed, easily removed for inspection, repair or replacement of the insulated flange or fitting, and which for safety reasons permits rapid and positive detection of fluid leakage from the flange or fitting.